MILWAUKEE (Reuters) - Milwaukee lawmakers on Tuesday approved a $124 million plan to build a downtown streetcar system, which supporters say will spur economic growth and opponents call a waste of money.

City council members voted 9-6 not to reconsider its January approval of the streetcar project, which will be funded through federal grants and tax incremental districts. It is scheduled to be completed by 2018.

Milwaukee will join several other U.S. cities that have streetcars including Portland and Seattle. A similar streetcar system, costing $133 million, is under construction in nearby Cincinnati.

The plan is to start with four cars and a 2.5-mile loop through downtown Milwaukee. Eventually, the system will extend to Milwaukee's international airport 10 miles south of downtown and to the University of Wisconsin-Milwaukee three miles north, according to plan documents.

Supporters say a streetcar system will spur economic development by creating jobs and shape the identity of downtown Milwaukee.

The project "presents a once-in-a-generation opportunity to move our city forward and make Milwaukee more attractive to new employers, workers, residents and tourists," Greg Marcus, CEO of the Milwaukee-based Marcus Corporation, said in a statement.

Funding for the project is planned through federal grants totaling $64.9 million, contributions from an existing tax incremental district of $9.7 million and two proposed districts that are expected to generate $49.3 million, according to planning documents. A tax incremental district is an instrument used by municipalities in which increases in property tax revenue within the district are used to pay back capital improvement loans.

Opponents said the project is a waste of money for Milwaukee, which struggles to fill potholes and regularly requires police to take furlough days.

"I think this is financially a terrible move for the future of the City of Milwaukee," council member Tony Zielinski said.

Citizens For Responsible Government, which opposes the project, has launched a petition drive aimed at forcing the city to hold a binding referendum on the plan. They must gather 31,000 signatures by March 3 to force a public vote.